In a known paper currency deposit-withdrawal mechanism, during a pay-in transaction a regular banknote, which is an introduced banknote classified as a genuine note by a classification section, is stored in a denomination-specific banknote storage box whilst incrementing a stored note count. During a pay-out transaction, banknotes of denomination(s) that configure the payment amount are fed out from the corresponding banknote storage boxes one note at a time. These banknotes are classified by the classification section, and regular banknotes classified as genuine notes are conveyed to a paying in/paying out section and stacked whilst decrementing the stored note count of the banknote storage box. When all of the banknotes configuring the payment amount have been stacked at the paying in/paying out section, the banknotes are paid out to the customer. During pay-out, banknotes classified by the classification section as having conveyance irregularities such as overlapping travel or chains are conveyed to a reject box as reject banknotes and stacked, even if they are regular banknotes (see for example Japanese Patent Application Laid-Open (JP-A) No. 2010-287073 (paragraphs 0043 to 0054, 0068 to 0072, and FIG. 4)).